Manufacture of azodicarbonamide



United States Patent Ofilice 2,988,545 Patented June 13, 1961 2,988,545MANUFACTURE OF AZODICARBONAMIDE Henry A. Hill, Watertown, Mass.,assignor to National Polychemicals, Inc., Wilmington, Mass., acorporation of Massachusetts No Drawing. Filed Oct. 17, 1957, Ser. No.690,634 Claims. (Cl. 260192) Azodicarbonamide has been proposed as ablowing agent in the manufacture of cellular products from rubber andplastics. It is known to release nitrogen upon melting or decomposing,but objections such as high decomposition temperature, poor dispersion,residual color and ineflicient blowing have been raised. Yields of theproduct derived from a raw material so expensive as hydrazine have leftmuch to be desired.

The most effective use of azodicarbonamide as a blowing agent to producethe lowest density possible from a given amount or to obtain a givendensity with a minimum amount of the agent has not been achieved.Particularly in cellular products derived from vulcanized rubber fullusage of its blowing potential has not been achieved. Only partialdecomposition of the blowing agent. to release its nitrogen results andthe undecomposed azodicarbonamide can be extracted from the rubbercompound,

The principal objects of this invention are to overcome theafore-mentioned objections and to produce azodicarbonamide in a formwhich permits full utilization of its potential power to reduce thedensity of plastic and vulcanized rubber articles.

Further objects of this invention are to produce azodicarbonamide inessentially quantitative yields, to produce azodicarbonamide in a formwhich will decompose completely in vulcanized rubber articles thusremoving an undesired interference with the color of the rubber articlesproduced, and to produce azodicarbonamide in the form of microcrystals,the major dimension of which is of the order of one micron.

I have found that when azodicarbonamide is prepared by oxidizinghydrazodicarbonamide under certain conditions, particularly the controlof the temperature of the reaction mixture, the concentration of theoxidant and the ratio of oxidizing solution to the reductant, that I notonly attain greatly superior yields, but also a means of controlling theparticle size of the product to obtain a discrete microcrystallinestructure of the order of one micron or less in its major dimension, asdistinguished from the large aggregates which would otherwise beobtained. I have attained yields better than 98% of the theoretical, ascompared with 84% for certain known procedures. Such as that set forthin B.I.O.S. Final Report No. 1150 at page 23. Quite contrary toexpectations a more concentrated oxidant at lower temperature and aslightly longer reaction time gave both higher lyields and a many-foldsmaller particle.

As is known urea reactions with hydrazine or its salts to formhydrazodicarbonamide according to the following equation:

2NHiCONHQ+NzH4-HZSOr-- NH2OONHNHC o NHz-I-(N O2S or Urea HydrazineHydrazodicarbon- Ammonium sulfate amide sulfate The hydrazodicarbonamidereacts with oxidizing agents such as chromic acid or chlorine to formazodicarbonamide according to the following equation:

weight of hydrazodicarbonamide is suspended in two to four parts, byweight of water to form an aqueous slurry.

The hydrazodicarbonamide may, if desired, be prepared in accordance withknown procedures, but I prefer to synthesize it from hydrazine hydrate,monohydrazine sulfate or dihydrazine sulfate, urea and sulfuric acid, ashereinafter set forth.

After having formed the aqueous slurry, an alkali metal chromate isadded, such as potassium or sodium chromate, dichromate or polychromate,but irrespective of the particular chromate used the amount should besuflicient to effect oxidation of the hydrazodicarbonamide toazodicarbonamide. The oxidation takes place upon the addition ofsulfuric acid in an amount sufiicient to liberate CrO (chromic acid)from the chromate. Variations such as the use of chromium trioxide inthe presence of a non-oxidizing mineral acid or the addition of therequired amount of sulfuric acid followed by addition of a solid alkalimetal chromate or dichromate salt or chromium trioxide are within thescope of the invention.

When an alkali metal chromate or dichromate or a concentrated solutionthereof is added first, the subsequent addition of the acid should beslow, preferably extending over a period of one to two hours, and underno conditions should the rate of addition be such as to increase thetemperature above approximately 85 F. Accordingly, the reaction mixturemay be and preferably is refrigerated to maintain a temperature between32 and 85 F. Lower temperatures approaching the solidificationtemperature of the mass are operable but are less practicable. In anycase, this temperature range is held until all the reactants are addedto the reaction vessel. The temperature and conversion time areinversely related and although substantially complete conversion may beachieved while maintaining the above temperature range, it is at theexpense of eificient use of the production facilities. For example, bymaintaining a temperature of approximately 32 F., several days will berequired to achieve substantially complete conversion.

I have found that a family of forms of azodicarbonamide may be producedwithin the concentration and temperature limits hereinafter set forth.For example, I may hold the temperature at 32 F. throughout thereaction. I may run from 5 to 30% conversion at 32 F. then heat thereaction mixture to a maximum of about 150 F. to achieve completeconversion. I may run to about 30% conversion at 50, 65 or F., then heatthe reaction mixture to a maximum of about 150 F. to achieve completeconversion. I may run to any desired percentage conversion, i.e., to 50,60 or even 80% at a temperature below F., then heat the reaction mixtureto a maximum of about F. to achieve complete conversion.

If a time of two hours is selected for addition of dilute sulfuric acid,the percent converted at this time will vary from about 5% at 32 F. to25% at 75 F. If the temperature of the reaction mixture has beenmaintained at approximately 85 F. for two hours while adding dilutesulfuric acid and for two hours more and a conversion of 70 to 75%achieved, thereafter heating the reaction mixture at such a rate as toreach a temperature of approximately 150 F. in a period of one andone-half hours will result in substantially complete conversion.

In all these variations azodicarbonamide is produced in a formdefinitely superior to the product of the prior art and capable of beingused more eifectively as a blowing agent in rubber and plastics.

After having completed the reaction the insoluble azodicarbonamide maybe recovered by filtration, washed and dried in conventional manner.Certain additions such as mineral oils or ester type plasticizers,diluents, etc. may be made before or after filtration in accordance withrecognized practices of the art.

So long as the aforementioned conditions of time, temperature andconcentration are observed, the resulting yield of azodicarbonamide willbe approximately 98% of the theoretical and the product is characterizedby being a very light yellow color and in the form of discretemicrocrystalline particles, the major dimension of which is of the orderof about one micron which need not be ground or otherwise treated, ascontrasted with the orange or orange-red crystalline aggregates whichmust be ground even to pass a 325-mesh sieve (44 microns).

Examples illustrating the foregoing are as follows:

Example 1 A suitably jacketed 1,000-gallon enameled steel kettleequipped with a stirrer and reflux condenser was charged with 1,200pounds of dihydrazine sulfate (containing 14.1 moles of hydrazine),3,000 pounds of water and 3,500 pounds of urea (58.4 moles). Heating wasstarted and 712 pounds of sulfuric acid was added, advantage being takenof the heat of dilution to accelerate the approach to the refluxtemperature of approximately 220 to 230 F. While the mixture was held atthe reflux temperature, sulfuric acid was added until aniodide-titration test on the filtrate from a cooled sample of themixture indicated that all hydrazine had been converted tohydrazodicarbonamide in essentially quantitative yield. Approximately1425 pounds of sulfuric acid (13.50 moles) were required. The resultinghydrazodicarbonamide was in the form of an aqueous slurry and did nothave to be isolated for the practice of this invention.

The slurry was then cooled to about 70 F. after which 1,600 pounds ofsodium dichromate dihydrate were added. Thereafter, 4,000 pounds of 55%sulfuric acid were run in over a period of two hours while maintainingthe reaction mixture at essentially 70 F. by running cold water or brinethrough the jacket. At this point 20-30% azodicarbonamide conversion hadbeen achieved. The conversion is conveniently determined by a solubilityrelationship, i.e., hydrazodicarbonarnide is quantitatively insolublewhile azodicarbonamide is moderately soluble in dimethylsulfoxide. Thetemperature was held at essentially 70 F. for about two hours more atwhich time a conversion of about 50% had been achieved, as indicated bythe dimethylsulfoxide test, and then the reaction mass was heated atsuch a rate that a temperature of 150 F. was attained in one andone-half hours, at the end of which 100% conversion had taken place,giving a 98% yield of azodicarbonamide.

Example 2 A slurry containing 100 parts of hydrazodicarbonamide wasprepared in the manner set forth in Example 1 and was cooled to about 32F. After adding 100 parts of sodium dichromate dihydrate, 250 parts of55% sulfuric acid were added over a two hour period, While the reactionmixture was maintained at a temperature between 32 and 35 F. The mixturewas heated to 150 F. in 1.6 hours at which time conversion was complete.

Example 3 Following B.I.O.S. Final Report No. 1150 at page 23, 90 partsof hydrazodicarbonamide was added to 660 parts of 20% sulfuric acid andthe mixture oxidized by addition of 89 parts of sodium dichromate(solid) during one hour at 122 F. The mixture was then stirred at 140 F.for one hour after which the product was filtered off and washed withwater until neutral. Yield was. 77 parts equivalent to 84% of thetheoretical.

Example 4 A slurry of hydrazodicarbonamide was prepared in the mannerset forth in Example 1. The slurry was cooled to about 95 F., then 1,600pounds of sodium dichromate dihydrate were added, then 4,000 pounds of55% sulfuric acid were added over a period of one and one-half hours,while the temperature was held between 97 and 102 F.

4 by external cooling. The mixture was held between 97 and 102 F. fortwo hours additional then heated to F. over a period of two hours. Theazodicarbonamide was isolated in the usual manner and was found to be inthe form of crystal aggregates with an orange red color.

Example 5 A rubber compound designed for a low-gravity shoe soling stockwas used to illustrate the properties of my blowing agent. A masterbatchwas made from the following:

Ingredients Parts Styrene-Butadiene Rubber 1010 a 85.0 Styrene-BntedieneRubber 1006 15.0 Styrene-Butadiene Resin 0 15. 0 Cumarone-Indene Resin(soft pt. 220 F.) 10.0

were mixed on a rubber mill at 220250 F.. the mill was cooled to -180 F.and then there were a lcled Stearic Acid 4. 0 OctylatedDiphenylamine. 1. 0 Hydrated Silica 30. 0 Soft clay 70.0 Ground whitin25.0 Titanium Dio 15.0 Zinc Oxide 5. 0 Light process oil 15.0 DiethyleneGlycol variable Portions of the masterbatch in the proportions givenabove were mixed on a rubber mill at 120-30 F. with B Styrene 23.5parts, butadiene 76.5 parts polymerized at 122 F. Mooney viscosity (MLat 212 F.) 30.

b Styrene 23.5 parts, butadiene 76.5 parts polymerized at 122 F.',contains a non-staining antioxidant, Mooney viscosity (MIA at 212 F.)

the masterbatch which has a specific gravity of 1.34 beforevulcanization.

A B O D E F Azodicarbonamide. Ex. 1 Ex. 3 Ex. 1 Ex. 3 Ex. 1 Ex. 3 Partsper 100 parts Rubber Hydro ll l3 l2 13 13 13 30 F 15 15 15 15 15 15Specific Gravity,

70 F./70 1 1..-". 0.12 0.32 0.18 0.37 0.27 0. 39 Percent Expansion l,015 319 615 262 306 244 Percent Expansion per part blowing agent 81. 225. 4 64. 5 26. 2 49. 5 30. 7

e Percent expansion=Final volume-Initial volume Initial volume Tests Ato F contained 1.0 part diethyleneglycol per 100 parts of rubberhydrocarbon.

It is seen that azodicarbonamide prepared according to this inventiongives greater than a three-fold reduction in density than the previouslyknown product and that eight (8) parts of azodicarbonamide preparedaccording to this invention produces a lower specific gravity than 12.5parts of the previously known product.

Example 6 A series of tests was made, using the master batch prepared inExample 5, to show the effectiveness of azodicarbonamide preparedaccording to this invention with and without an activator such asdiethyleneglycol.

G H J K L M Azod1carbonamide-. Ex. 1 Ex. 3 Ex. 1 Ex. 3 Ex. 1 Ex. 3 Partsper 100 parts Rubber Hydrocarbon 9. 9. 0 8.0 12.0 8. 0 12. 0 DiethyleneGlycoL- 1. 0 1. 0 Hardness (Shore A). 20 25 32 27 .38 38 SpecificGravity,

70 F./70 F-.-.... 0. 19 0. 34 0. 24 0.28 0.31 0. 31 Percent Expansion-606 295 459 379 332 329 Percent Expansion per part of blowing agent 67.4 32.8 57. 4 31. 6 41. 27. 4

Tests G toM cured 13 minutes at 315 F.; minutes at 307 F.

Tests G and H show that at equal weights azodicarbonamide preparedaccording to this invention gives 300% greater expansion than theproduct of the prior art. Tests I and K show'that eight (8) parts ofazodicarbonamide prepared according to this invention gives 80% greaterexpansion than twelve (12) parts of the product of the prior art,although the state of cure is higher in the former compound. Tests -Land M show that eight (8) parts of azodicarbonamide prepared accordingto this invention gives an expansion equal to the expansion given bytwelve (12) parts of the product of the prior art at the same state ofcure.

Example 7 A rubber compound designed for a medium gravity shoe solingstock was used for further illustration of the properties ofazodicarbonamide made according to this invention. A master batch wasmade from the followmg:

Ingredient Parts Styrene-Butadiene Rubber 1502 65. 0 Styrene-ButadieneRubber 1703 b 44. 0 Styrene-Butadiene Resin e 45 0 Pentachlorothi 1 0were mixed on a rubber mill for 7.5 minutes at 270 F. The

mill was cooled to 220 F. and then was added- Cumarone-Indene Resin(soft pt. 220 F.) 7. 5

The temperature was held at 180-l90 F. and then were added in tenminutes to complete the masterbatch- Octylated Diphenylamine StearicAcid- Hard Clay Hydrated Silica Light Process Oil- Zinc Oxide TitaniumDioxide- The mill was cooled to l130 F. and then were added to portionsof the masterbatc Diethylcne GlyccL- variable Dibenzothiazyldisulfide L8 Diorthotolylguanidine 0. 3 Azodicalbonamide L 0 Sulfur 3. 5

The compounds were cured thirteen (13) minutes at 315 F. and fifteen(15) minutes at 307 F.

l Styrene 23.5, butadiene 76.5 polymerized at 43 F. to a Mooneyviscosity (ML4 at 212 F.) of 50.

b Styrene 23.5, butadiene 76.5 polymerized at 43 F. to a MooneyViscosity (ML4 at 212 F.) of 60, and oil extended with parts per 100 oflnaphthenic processing oil.

Styrene 85 parts, butadiene 15 parts copolymer.

Mooney viscosity (ML4 at 212 F.) 30.

Tests N, 0, P and Q show again the superior results fromazodicar-bonamide made according to this invention as regards percentageexpansion and cell structure.

Example 8 A rubber compound designed for general usage was prepared forfurther illustration of the properties of azodicarbonamide madeaccording to this invention. A master-batch was made from the following:

e Styrene 235 parts, butadiene 76.5 parts polymerized at 122 F.;

Portions of the masterbatch in the proportions given above were mixed ona rubber mill at F. to -F. with the following:

Diethylene glycol 1.0 Dibenzothiazyldisulfide 0.75 Diorthotolylguanidine0.25 Azodicarbonamide variable Sulfur 3.0

R S T U Azodicarbonamide Example Examplg Example Example 3 Parts perhundred Rubber Hydrocarbon 7. 5 7. 5 4.0 4. 0 1st cure: Min. at 315 F-12 12 13 13 2nd cure: M111. at 307 F-.... 15 15 15 15 Specific Gravity,70 F./70 F. 0. 19 0. 90 0.56 1. 01 Percent Expansion 606 49 139 33Percent Expansion per part of blowing agent 80.9 6. 53 34. 8 8.25

Example 9 Ingredient Parts Pale Crepe 80. 0 Styrene-Butadiene Rubber1006 20. 0 Styrene-Butadiene Resin 20.0 Zinc Pentochlorothiophenolate0.3

were mixed in a rubber mill five minutes at 230 F., then cooled to 212F. and was added- Gumarone-Indene Resin (soft pt. 220 F.) 5 0 the millwas cooled to F. and in 1214 minutes were added- Soft Clay. 60. 0Hydrated Sodium Silico Aluminate 30.0 Whiting 20.0 Titanium Dioxide.15.0 Zinc Oxide 5. 0 Light Processing Oil- 10.0 Stearic Acid 2. 0Octylated Diphenylamme 2.0

The masterbatch had a Mooney viscosity (ML4 at 212) of 40.

a Styrene 23.5, butadiene 76.5 polymerized at 122 F. to Mooney viscosity(ML4 at 212 F.) of 50.

b Styrene 85 parts, butadiene 15 parts copolymer.

To 269.3 parts of the masterbatch was added 10 parts azodicarbonamideand 0.4 parts tetramethylthimiamdisulfide and 3.5 parts sulfur. Cure was12.5 minutes at 307 F. and five (5) hours at 212 F.

Test V W Azodiearbonamide Example 1 Example 3 S ecific Gravity, 70 F./70F 0.25 0. 84 ardness (Shore A) 25 57 Percent Expansion 435 58 PercentExpansion per part blowing agent. 43. 5 5. 8

Example 10 Portions of the masterbatch described under Example 5 weremixed with the accelerators and blowing agents and cured as indicated:

At the same state of cure only half as much of an azodicarbonamide ofthis invention is required to produce a lower specific gravity than thepreviously known product.

I claim:

1. The process of producing azodicarbonamide, which comprises suspendingapproximately one part, by weight, of hydrazodicarbonamide in two to ourparts, by weight, of water to form an aqueous slurry, adding to saidslurry an alkali metal chromate in an amount at least suflicient toeffect complete oxidation of the hydrazodioarbonamide, slowly addingdilute sulfuric acid to said slurry in an amount sufiicient to liberatethe CrO from said chromate and to effect oxidation of the hydraz0-dicarbonamide to partially convert the hydrazodicarbouamide toazodicarbonamide while maintaining the reaction mixture at a temperatureof approximately 85 F., thereafter heating the reaction mixture to atemperature between 110 and 150 F. until approximately completeconversion to azodicarbonamide has been achieved, and

finally filtering, washing and drying the azodicarbonamide thusproduced.

2. The process of producing azodicarbonamide, which comprises reactingurea, a hydrazine sulfate and sulfuric acid in water to form an aqueousslurry of hydrazodicarbonamide containing approximately one part byweight of hydrazodicarbonamide in two to four parts by weight of water,adding to said slurry an alkali metal chromate in an amount at leastsufficient to effect complete oxidation of the hydrazodicarbonamide,slowly adding dilute sulfuric acid to said slurry in an amountsufiicient to liberate the CrO from said chromate and to efi'ectoxidation of the hydrazodicarbonamide to partially convert thehydrazodicarbonamide to azodicarbonamide while maintaining the reactionmixture at a temperature not exceeding 85 F., thereafter heating thereaction mixture to a temperature not exceeding 150 F. untilapproximately complete conversion to azodicarbonamide has been achieved,and finally filtering, washing and drying the azodicarbonamide thusproduced.

3. The process of producing azodicarbonamide, which comprises reactingurea, a hydrazine sulfate and sulfuric acid in water to form an aqueousslurry of hydrazodicarbonamide containing approximately one part byweight of hydrazodicarbouamide in two to four parts by weight of water,adding to said slurry an alkali metal chromate in an amount at leastsufiicient to efiect oxidation of the hydrazodicarbonamide, slowlyadding dilute sulfuric acid to said slurry in an amount sufiicient toliberate the Cr0 from said chromate and to effect oxidation of thehydrazodicarbonamide to partially convert the hydrazw d-icarbonamide toazodicarbonamide while maintaining the reaction mixture at a temperaturebetween 32 and F., thereaiiter heating the reaction mixture to atemperature between approximately and F. until approximately completeconversion to azodicarbonamide has been achieved, and finally filtering,washing and drying the azodicarbonamide thus produced.

4. The process of producing azodicarbonamide, which comprises suspendingapproximately one part by weight of hydrazodicarbonamide in two to fourparts by weight of water to form an aqueous slurry, adding to saidslurry an alkali metal chromate in an amount at least suflicient toeifect complete oxidation of the hydrazodicarbonamide, slowly addingdilute sulfuric acid to said slurry in an amount suflicient to liberatethe CrO from said chromate and to efiect oxidation of thehydrazodicarbonamide to partially convert the hydrazodicarbonarnide toazodicarbonamide, while maintaining the reaction mixture at atemperature not exceeding about 85 F. until at least a partialconversion to azodicarbonamide has been achieved, and thereaftermaintaining the reaction mixture at a temperature not exceedingapproximate- -ly- 150 F. until approximately complete conversion toazodicarbonamide has been achieved, and finally filtering, washing anddrying the azodicarbonamide. 5. The process of producingazodicarbonamidewhich comprises suspending approximately one part byweight of hydrazodicarbonamide in two to four parts by weight of waterto form an aqueous slurry, maintaining the temperature of the slurry atno higher than 85 F. While incorporating OrO and a non-oxidizing mineralacid in theslurry at a rate such that the temperature does not exceed 85F. and in amounts sufficient to effect complete oxidation of thehydrazodicarbonamide to convert hydrazodicarbonamide toazodicarbonamide, maintaining the reaction mixture at a temperature notexceeding 85 F. until at least partial conversion to azodicarbonamidehas been achieved, there-after maintaining the reaction mixture at atemperature not exceeding approximately 150 F. until approximatelycomplete conversion to azodicarbonamide has been achieved and recoveringthe azodicarbonamide.

6. The process defined by claim 5 wherein after partial conversion toazodicarbonamide has been achieved the reaction mixture is heated to atemperature between 110-150" F.

7. The process defined by claim 5 wherein the aqueous slurry ofhydrazodicarbonamide is formed by reacting urea, a hydrazine sulfate,and sulfuric acid in water.

8. The process defined by claim 5 wherein the reaction mixture is heatedto a temperature not exceeding approximately 150 F. in a period of lessthan one and one half hours.

9. The process defined by claim 5 wherein between about 5 and 80 percentconversion to azodicarbonamide is achieved while maintaining thereaction mixture at a temperature not exceeding about 85 F.

10. Azodicarbonamide formed by the process defined by claim 5.

References Cited in the file of this patent (Library

1. THE PROCESS OF PRODUCING AZODICARBONAMIDE, WHICH COMPRISES SUSPENDINGAPPROXIMATELY ONE PART, BY WEIGHT, OF HYDRAZODICARBONAMIDE IN TWO TOFOUR PARTS, BY WEIGHT, OF WATER TO FORM AN AQUEOUS SLURRY, ADDING TOSAID SLURRY AN ALKALI METAL CHROMATE IN AN AMOUNT AT LEAST SUFFICIENT TOEFFECT COMPLETE OXIDATION OF THE HYDRAZODICARBONAMIDE, SLOWLY ADDINGDILUTE SULFURIC ACID TO SAID SLURRY IN AN AMOUNT SUFFICIENT TO LIBERATETHE CRO3 FROM SAID CHROMATE AND TO EFFECT OXIDATION OF THEHYDRAZODICARBONAMIDE TO PARTIALLY CONVERT THE HYDRAZODICARBONAMIDE TOAZODICARBONAMIDE WHILE MAINTAINING THE REACTION MIXTURE AT A TEMPERATUREOF APPROXIMATELY 85* F., THEREAFTER HEATING THE REACTION MIXTURE TO ATEMPERATURE BETWEEN 110* AND 150* F. UNTIL APPROXIMATELY COMPLETECONVERSION TO AZODICARBONAMIDE HAS BEEN ACHIEVED, AND FINALLY FILTERING,WASHING AND DRYING THE AZODICARBONAMIDE THUS PRODUCED.